From DE 4335004 A1, DE 20013047 U1 and DE 10060013 A1 there are known what are called film potentiometers. In these potentiometers, the substrates of the resistive elements and of the contact electrodes are made of film material. Between the substrates there is mounted a spacer of film material, thereby creating the insulating distance between the resistive element and the contact electrode.
To actuate a film potentiometer, the substrates of the resistive element and of the contact electrode are pressed together. This is usually done by pressing down on the substrate of the contact electrode, which for this purpose can be actuated by the finger or urged by a plunger.
When the substrates of the resistive element and contact electrode are pressed together, dimples are formed in the film material, which dimples recover only slowly and sometimes not completely. All common film material have a more or less pronounced temperature dependence in their recovery behavior, the film becoming more plastic with higher temperatures. Because of the temperature dependence of the recovery behavior, the linearity of the potentiometer can be impaired.
In a pressure-actuated potentiometer according to WO 2007/016281 A2, a shielding material is fastened to the surface on which actuating pressure is exerted. This material is supposed to improve the functional performance and reliability of the potentiometer in the high-temperature range and under the wear conditions to which the potentiometer is subjected by the actuating pressure. Boron silicate and glass fibers are mentioned as particularly durable and heat-resisting shielding materials.